A polymer having a hydrophilic group such as a sulfonic group is expected to find use in a wide variety of applications.
In addition, the synthesis of such a polymer containing a sulfonic group is generally limited to one involving the use of a specific vinyl monomer containing a sulfonic functional group. Specific examples of the monomer include sulfonated styrene and AMPS(2-acrylamide-2-methylpropanesulfonic acid) (for example, see JP-A 2002-351147).